Symbology Support

Also see XMLConfigReference for descriptions of these elements within the xml mapfile.

Styles

Named styles, each layer can reference 0...N styles.

Order is important -- as in the 'painter model' or Painter's algorithm to be specific. Layers that are declared first in your XML file, or added programmatically through Layer::add_style are drawn first. Layers that are declared or added later are drawn last.

Rules

Each style can have 0...N rules. Rules can have min/max scale denominators <someone explain min/max denom here!> and filter expressions.

Filters

Syntax for filter expressions is very simple, you enclose variables (evaluated at runtime) in square brackets: [attribute_name].

Support for:

Arithmetic: +, -, *, /
Comparison: >, <, =, <>, >=, <=
Logical operators: and, or, not
Regular expression matching: [attribute_name].match('reg_ex')

See Filter for more details (especially regarding how this is different for XML).

Symbolizers

Symbolizers describe how features appear on a map.